Ongoing Research in Communication Technology Laboratory

1. Ongoing Research in Communication Technology Laboratory Information Engineering Department The Chinese University of Hong Kong Prof. Tak-Shing Peter Yum (任德盛 教授)

2. Outline • Internet • Congestion Control (Cun-Qing Hua) • Peer-to-Peer Network (Li Zhang) • Internet Content Adaptation Protocol (Wing-Lam Tam) • Wireless Communication • OVSF Code Assignment Schemes (Yang Yang) • Cell Sectoring for CDMA Systems (Fang-Zhong Shen) • Routing • Offline Routing for RPR (Cheng Li)

3. Congestion Control – 1 • Host-based Congestion Control • Based on packet loss detection: e.g. TCP Tahoe, Reno and NewReno • Based on end-to-end delay variance: e.g. TCP Vegas and Tri-S • Advantages • Easy to implement • Easy for decentralized resource allocation • Weakness • long response delay (at least one round trip time) • Limited information collected solely from end hosts may lead to improper response to congestion

4. Congestion Control – 2 • Case study: TCP Vegas The TCP Vegas flows passing through multiple congested links tend to be unfairly treated due to the cumulative nature of round trip time • Router-based Congestion Control • Routers monitor the network state and notify the end hosts in case of congestion by dropping or marking packets: e.g. RED, BLUE, ECN

5. Congestion Control – 3 • Our solution:The Joint Congestion Control (JCC) • It unifies the efforts of end hosts and routers to provide proactive and accurate congestion control • Basic Idea The source sends probing packets to collect the state of the most congested link along the path, and with which to adjust the congestion window • Properties • Lower variance of throughput • Lower packet loss rate • Fairer resource allocation

6. Peer-to-Peer Network – 1 • Traditional C/S Model • P2P network: • every node can take the roles of both server and client • intermittently connected edge devices (PC, PDA, WAP Phones) can receive information from and provide information to the Internet • Takes advantage of edge device resources • Storage and processing capability of edge devices • Content of edge devices • Human presence at edge devices

7. Peer-to-Peer Network – 2 • Typical Problems • A distributed naming scheme for nodes and files • A distributed file indexing scheme • Server selection • A distributed routing protocol (reverse anycast) • Security and authentication

8. Peer-to-Peer Network – 3 • Our work • Architecture and topology • Architecture design: Distributed, Centralized and Augmented • Network partitioning • Server selection • Network distance Measures • Routing rules • Delay and throughput Analysis

9. OVSF Code Assignment Schemes– 1 • Orthogonal variable-spreading-factor(OVSF) codes are the basic resource units for assignment in UTRA-TDD and FDD systems

10. OVSF Code Assignment Schemes– 2 • Nonrearrangeable and rearrangeable code assignment schemes • Our solution:Compact Assignment (CA) and Rearrangeable Compact Assignment (RCA) • Both schemes can leave the resulting code tree as flexible as possible (in supporting multi-rate traffic classes) after each code assignment • Analytical and simulation results show both schemes can offer the blocking, throughput and fairness performance very close to the theoretical bounds • Compared with other schemes, CA and RCA have the combined advantage of simple, efficient, stable and fair • Generalization: optimize the assignment to match the traffic rate distribution

11. Cell Sectoring for CDMA Systems– 1 • Problem • Cell sectoring is used to reduce the co-channel interference • However, it works inefficiently when addressing hot-spot scenarios. Some congested sectors may have outages, while the lightly loaded sectors may have spare capacity • Solution • Dynamic cell sectoring, i.e., adaptively changing the sector pattern according to the traffic can solve the problem

12. Cell Sectoring for CDMA Systems– 2 • Three Aspects • How to produce dynamic sector patterns? • Circular Array Beamforming networks with Butler Matrix • Dynamic Cell Sectoring Algorithms • MinTTP Sectoring based on Shortest Path Algorithm • PE Sectoring based on Greedy Algorithm • How to keep the optimality of the sectoring at all times • Resectoring: Detect the traffic and readjust the sector boundaries when necessary.

13. Internet Content Adaptation Protocol– 1 • Objective • Develop Web services for customizing content • Language Translation • Advertisement Insertion • Conventional Approach • Proprietary API • Single-source solution, creating programming and testing complexities • Problems of scalability, flexibility, reusability

14. Internet Content Adaptation Protocol– 2 • Our Approach • Attach application servers to proxies through ICAP

15. Internet Content Adaptation Protocol– 3 • Internet Content Adaptation Protocol • Open protocol • Enables communication between edge content devices (web caches and Internet content origin servers) and application servers for content adaptation • Part of an evolving architecture that promotes Web scalability by better facilitating distribution and caching

16. Internet Content Adaptation Protocol– 4 • Work Involved: • Development of the ICAP protocol core • Architecture design • Software implementation • Development of the ICAP-enabled e-services • Content filter and transcoder for WAP phones • Advertisement insertion server • Performance analysis of ICAP-enabled proxy • ICAP overhead • System scalability, efficiency • Caching performance

17. Offline Routing for RPR – 1 • The topology of IEEE 802.17 Resilient Packet Ring (RPR) is as follows

18. Offline Routing for RPR – 2 • Objective • Design the link capacity dimensioning for this system • Problems • Given: Traffic matrix, Ring topology, utility function • Maximize the system revenue or throughput while maintain fairness among the competing flows • Given: Traffic matrix, utility function • Link capacity dimensioning • Solutions: • Linear programming • Non-linear programming with convex objective function and linear constraints